Fuel cell systems are known as generating devices to take out electric energy generated after electrochemical reaction between fuel and oxidant. An electrolyte module such as a proton-exchange membrane is positioned between a cathode and an anode, and at both sides of the electrolyte module a separator (separator plate) with gas flow channels is arranged respectively to form a unit (cell). In fuel cell systems, a number of such units (cells) are laminated as a fuel cell stack.
Because the separator electrically connects adjacent cells, it is required to have excellent conductivity. Also, because cooling water flows through the separator, it is required to have corrosion resistance. As conventional separators, for example, Japanese Laid-open Patent Application Nos. 11-126620, 11-162478, 2000-36309, and 2000-297780 disclose carbon-made separators such as made of fine carbon graphite and carbon plate, or metal separators such as made of stainless steel.
The separator made of fine carbon graphite excels in conductivity. However, it becomes heavy and thick. Further, because fine carbon graphite is a very fragile material, it is very difficult to apply cutting operations to form a number of protrusions on the surface of the separator for the provision of gas flow passages. This leads to increase in the processing cost.
In the case of the separator made of a carbon plate, it is inferior in conductivity. Further, because carbon plates are not suitable for press working. Therefore, gas flow passages are formed by cutting operations. This leads to increase in the processing cost and weight.
In the case of the metal separator such as made of stainless steel, because such a metal is inferior in corrosion resistance and acid resistance, the separator requires a surface treatment such as by gold plating or platinum plating. This leads to less effective productivity and increase in the production cost. Metal can be used for press working and can be decreased in thickness. However, because of its inferior workability, the production method of gas flow passages undergoes some restrictions, such as a requirement in fine seal. If gas flow passages are formed by etching, the separator becomes heavy and costly.
In view of the above, the present invention seeks to provide a separator which is small and light in weight, and excels in corrosion resistance and conductivity.